Method of and means for detecting defects in paramagnetic material



W. E. HOKE.

METHOD 0F AND -MEANS FOR DETECTING DEFECTS IN PARAIVIAGNETIC MATERIAL.APPLICATION FILED JUNE 255, 1919.

l A26588 Patented LAug. 22, 1922a Umf'rflau'l STATES vvPa'lENT orifice.

WILLIAM E. HKE, OF WASHINGTON, DISTRICT 0F COLUMBIA.

METHOD OF'AND MEANS FOR DETECTING DEFECTS IN PARAMAGNETIC MATERIAL.

T o' all wko'm t 'my concern.'

Be' itknown that I, WILLIAM E. HOKE,

a citizen of the United States, residing at -Washington, Districtof'Columbia, have invented certain new and useful Improvements vinMethodsof andMeansfor Detecting Defects in Paramagnetic Material, ofwhich the following is a specification.

This invention relates to a method of and means for detecting flaws,cracks, discontinuities of any kind and strains in iron, steel and otherparamagnetic materials.

In objects of iron, steel or other paramagnetic materials, the presenceof cracks, iiaws, discontinuities, stralns, etc., will have an'influence on the lines of magnetic flux setup by any cause in thematerial either through the agency of an external magnetizing force orsome permanent magnetism in the objects,

or from the natural field of the earth. `When such cracks, flaws,discontinuities, strains, etc., are at or near the surface of thematerial they affect the magnetic lines of iux on the surface.

It is the general object of. the invention to provide a method of andmeans for detecting the presence of defects of the character abovereferred to.

It is a particular object to detect defects which are too small to bereadily observable by ordinary means or even with aid of the microscope.i

It is the special object of the invention to detect defects by theutilization of the effects of a magnetic field at or near the surface ofobjects of paramagnetic material. u t

The invention briefly stated conslsts 1n subjecting a body to beexamined to the action of a magnetic field in the presence of a finelysubdivided magnetic medium.

For a fuller understanding of the principles upon which the applicationis based, reference is had tothe accompanying drawngs in whichV ig. 1 isa plan view of a gage showing cracks;

Fig. 2 is a similar view showing finely Y divided particles of magneticmaterial attached to the gage under the' influence of a magnetic field;

Fig. 3 is a sectinal view of a gage showv ing the action of a magneticeld upon a crecked gage in the presence of a finely divided ma neticmaterial v Fig. 4 1s a diagrammatic view of a gage placed in a magnticfield in a bath contain- Specification of Letters Patent.

ing finely divided paramagnetic material in sus ension; and ig. 5 is alan view vof a tray for simultaneously subjecting a plurality of gagesto the action of a magnetic field in a bath containing suspendedparticles.

Fig. 1V represents a gage lcontaning for Patented Aug. 22 1922.Application filed June'28, 1919. Serial No. 305,955. i i A the purposeof illustration four cracks.

These cracks are usually not `visible to the eye and ordinarily notobservable even under a microscope.

When however, the gage or other body of paramagnetic material is placedin a mag- 'netic field and paramagnetic material in a state of finesubdivision is brought in prox-4 imity to the surface of the body underexamlnatlon, part of the fine particles will cluster upon a crack orcracks that mayl exist and form a distinct observable mark,

vas indicated in Figs. 2 and 3.- This phenomf enon is probably uetomagnetic induction, the portions of the` body separated by the crackforming poles of opposite sign and the filings or other paramagneticparticles tending to closethe gap like the armature of a magnet.

If the body to be examined is of fairly soI hard iron or steel, themagnetic field may be produced by merely magnetizin the body in any ofthe usual Ways. If the' ody is of soft iron', -it'is'necessary toproduce a magnetic field and place the body into such field duringexamination'.

While the object of the invention may be carried out in various ways so.far as the bringing of the finely divided material into v pro'xlmity tothe surface of a body is concerned, I preferably suspend the finefilings in a fiuid medium and surround the body by the Huid holding theparticles in sus nsion.

When under such conditions the od is placed in a magnetic field, theforce o attraction exerted by the lines of force bridging the cracks issufficient to draw the particles fioating in proximity to the crack, tothe surface of the body to close the ma etic gap while near other partsof the bo y the magnetic lines pass trough the body within the surfacethereof'and therefore do not disturb the statical condition of thefloating particles or at least not to the saine extent or with the sameresult. At any rate, whatever may be the correct theory in explanationof the phenomenon, the presence of cracks,

sflaws, discontinuities -of any kind and strains, causes a non-uniformdeposit of the particles held in suspension in the fluid upon thesurface of the body under the lnfluence of the magnetic field.

lt is of course possible to hold particles in a state of suspension invarious fluids and in various Ways. So far as the broad conception ofprinciples governing the invention goes, it is not essentlal Wnat theparticular fluid and incidents of suspenslon ma be. l

have found that a liquid, such as o1l, of a specific gravity to hold thepartlcles 1n a state of equilibrium, or nearly so, gives fullsatisfaction. lt is not necessary that the liquid be such as to normallykeep the particles in suspension for an lndefimte period. lt issufficient and even referable for the purposes of the invention 1f theparticles are normally kept in a state of suspension during a periodwhich corresponds to the period of the test.

In F ig. 4 is diagrammatically shown a tray or pan of diamagneticmaterial to receive the liquid containing the line paramagneticparticles in suspension. 0n opposite sides of the tray are providedelectrol magnetic means including cores 6 and 7 and solenoids. 8 and 9respectively energized by current from a suitable source of supply, suchas a battery 10. The body 11 to be examined is immersed in the liquidand subject to the action of the magnetic field.

lnFig. 5 is shown a tray or pan 12 of 'sufficient size to receive arelatively large number of gages or other bodies to l be tested. lt is.understood that, as shown in F ig. 4, electromagnetic means are providedto cause a magnetic flux or magnetic lines of force to traverse thebodies contained in the pan 12.

It may be found advantageous to employ as a detecting mediumparamagnetic material having colorific properties to more distinctlymark the place of discontinuity.

ln practice vl4 provide the pan 12 with means (not shown) for drainingo' the liquid. rll`he magnetic ux is maintained Laaeea util the liquidhas been completely drained o ln the fore oing, l have referred to gagesas objects un er examination. Whilel the invention is primarily intendedfor testing small objects such as gages, balls, dies, etc. v

and for the detection of normally invisible defects of the charactermentioned, l am fully aware that the invention is of broader scope andapplicable to other purposes.

l claim:

1. The method of testing an object of paramagnetic material, Whlchconsists in subjecting the object to the action of a magnetic fieldWhile in proximity to mobile finely divided paramagnetic material.

2. 'llhe method of testing an object of paramagnetic material, whichconsists in subjecting the object to the action of a magnetic field in"afluid medium containing particles of paramagnetic material -insuspension.

3. The method ofv testing an object of paramagnetic material, whichconsists in sub'ecting the object to the action of a magnetlc field in aliquid medium containing particles of paramagnetic material` insuspension.

Il. rThe method of testing an object ofparamagnetic material, whichconsists inparamagnetic material, Whlch consists in' holding finelydividedwparamagnetic material in a state of suspension near a surface ofthe object and passing magnetic lines ofv force through said object.

6. An apparatus for testing paramagnetic' material, comprising areceptacle containin a medium holding paramagnetlc matena 1n suspenslonand means for passlng magnetic lines of force through the said me dium.

lin testimony WhereoflI ax my signature.

Willi AM' E. HUKE.

